The present invention relates to earth drilling machines, and more particularly, to an improved method and apparatus for driving and supporting drill strings.
Earth drilling machines are commonly used for drilling blast holes that are associated with strip mining, highway construction, and the like, or, for the drilling of water wells, as well as other uses. Known rotary earth drilling machines (such as those shown and described in U.S. Pat. Nos. 2,309,999; 2,849,212, 2,904,310; and 3,754,605) basically comprise a mobile frame, a mast pivotally mounted on the frame, a rotary drive carried on the mast, a drill pipe (or string of pipes connected together) connected at one end to the rotary drive and having its other end supporting a drill or other pipe bit and means for raising and lowering the rotary drive and therewith the drill pipe and its associated drill bit. Such arrangement of components, coupled with a conventional power means, provides both torque and downward force on the drill bit to thereby bore a hole in the earth. It should be pointed out here, that throughout this specification, a drill string means a drill pipe or series of drill pipes connected together.
Generally, in the majority of drilling operations, the mast is positioned in a generally vertical upright position; however, the mast may be positioned at any desired angle from horizontal to vertical during the drilling operation such as shown in U.S. Pat. No. 2,255,241.
Initially, in the drilling process, the rotary drive is positioned at the top of the mast with the drill pipe projecting downwardly therefrom to the attached drill bit which is resting on the top of the ground. Upon operation, the drive is rotated, imparting rotational movement to the drill pipe and the drill bit. Simultaneously therewith, the rotary drive is lowered along the mast, thus providing a downward force on the drill bit.
As the maximum length of the drill pipe, of the prior art drilling machines, is generally limited to the height of the drill mast, the depth of a bore hole is limited to the length of a single drill pipe; however, if the desired bore depth is to be greater than the single drill pipe, it is necessary to add additional drill pipes to the first drill pipe, thereby forming a drill string. Such operation requires the rotary drive to be disconnected from the initial drill pipe, raised to the top of the mast, at which time another drill pipe is introduced between and connected to the rotary drive and the first drill pipe. The above drilling process is then repeated until the desired bore depth is obtained. Sometimes, this requires the drill pipe connect-disconnect steps to be repeated several times. After the desired bore depth is reached, the drill string is removed from the bore hole and the drill pipes are disconnected separately. This drill pipe/string removal operation may be accomplished in many ways; for example, one way is by the utilization of a winch and pulley arrangement on the top of the mast. Such prior art drilling technique of connecting and disconnecting drill pipes involves a large amount of time and labor which considerably adds to the cost of drilling each hole. One way to decrease the number of connect-disconnect steps is to use a larger drilling machine with a higher mast; however, such machines are more expensive and more cumbersome to maneuver.